[EM] Multi-seat Condorcet

Steve Eppley seppley at alumni.caltech.edu
Mon Aug 16 06:27:12 PDT 2004


Warren Schudy asked:
> Does anyone know of a multiple-seat election method 
> that yields proportional representation if the number 
> of seats is large and the Condorcet winner if there's
> only one seat? Such a method would likely be better 
> than STV for small (<10) numbers of seats since IRV's
> flaws probably extend to STV, though a lesser extent. 
> It would also be helpful to defuse the argument that 
> IRV is better than Condorcet because it allows the 
> same system to be used for multi-winner and single-
> winner elections.

James G-A has already posted a reply containing a
link to Tideman's Condorcet/PR method so I won't
repeat it.

Another method that appears to meet Warren's spec is 
a variation of STV that never eliminates a Condorcet
winner.  Or that, when eliminating a candidate, 
eliminates the candidate that ranks lowest in 
the MAM social ordering.

I'm sorry to take a contrarian position I don't have 
the time to defend, but I'd like to add that I don't 
find the argument for PR compelling when PR is compared 
to the best alternatives.  Consider these alternatives:

1. (For electing a large legislature, too large for 
the voter to rank individual candidates.  A quasi-PR
system.)  Voters rank parties, not candidates.  
Each voter ranks the parties in order of preference.  
Each party is awarded seats in proportion to the number 
of voters who ranked it topmost, except a lot of extra 
seats are awarded to the party that would win if the 
votes were tallied by a good single-winner system 
(e.g. MAM). (The other exception is that, like in STV, 
votes for parties that are too unpopular to reach 
some threshold would count for their second favorite
parties, etc.)  In addition, the party that's
awarded the extra seats is also given the power
to unilaterally set the legislature's agenda and 
a veto over rule changes, and if a parliamentary 
system, a veto over the selection of cabinet 
officers (including prime minister).

2. (For electing a small legislature, small enough 
that each voter can rank most of the candidates.
An utterly non-PR system.)  Each voter ranks the 
candidates in order of preference.  The N candidates 
atop the MAM social ordering are elected.

I call a legislature "representative" if the policies
it adopts are similar to those the people themselves
would adopt if they had time to deliberate and vote
directly on the issues using a good voting method.

After a PR legislature is elected, the members still 
need to reach compromises, so I think the policies 
they adopt would tend to be similar to the policies 
that would be adopted using either alternative,
and similar to those the people themselves would
adopt if the people could deliberate and vote 
directly.  I see two key differences:  

1. The effects of vote trading, which would occur 
most with PR and least with alternative #2.  I can't 
predict whether the extra vote trading under PR
will be a net gain or loss for society.

2. I'm concerned that voters whose favorites aren't
centrist won't pay much attention to their favorites'
positions on the various centrist compromise policies 
that can pass the legislature, leaving too much room
for their favorites to be unaccountable and therefore 
more corrupt.


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